How can I "slideshow" between image textures on a plane?
You name all the images you want as a sequence, for example: image0001.png, image0002.png and so on. You can do this by importing them in Blender VSE and exporting all of them as pngs or you can do this using imagemagick.




Then in the shader, you import the first image. 



You change the value from single image to image sequence and set the number of frames to your total number of images.



Now the image sequencer will play all the frames from frame 1 automatically. If you want total control, set the start frame so that the last image of the sequence is the first image in the sequencer.



Now you can keyframe the offset value and change it however you want. You can hold on a frame or let it run as a sequence.